1. Field of the Invention
The present invention relates to a semiconductor device package, and more particularly, to a semiconductor device package, which can restrict a thermal stress caused between a semiconductor device that acts as a heating source and a package substrate that acts as a heat sink, and achieve an improvement in a heat emission property thereof.
2. Description of the Related Art
Generally, semiconductor device packages for light emitting diodes, laser diodes, or the like are designed and manufactured to fulfill the purpose of efficient emission of heat generated from semiconductor devices. In particular, since high-power light emitting diode packages used in the field of illumination emit a great amount of heat, a heat emission property is very important to the high-power light emitting diode packages.
To achieve an improvement in a heat emission property, it is generally proposed to use a package substrate, which is made of a material having a higher heat conductivity than that of constituent materials of a semiconductor device. FIG. 1 illustrates a simple exemplary configuration of a conventional light emitting diode package.
As shown in FIG. 1, the conventional light emitting diode package 10 comprises a package substrate 17 and at least one light emitting diode 15 mounted on an upper surface of the package substrate 17. The light emitting diode 15 includes a first conductive semiconductor layer 12, an active layer 13, and a second conductive semiconductor layer 14, which are laminated on a substrate 11 in this sequence from the bottom. The first and second conductive semiconductor layers 12 and 14 are provided thereon with first and second electrodes 16a and 16b, respectively, and in turn, the first and second electrodes 16a and 16b are connected to first and second bonding pads 18a and 18b on the package substrate 17 by use of wires.
The package substrate 17 is made of a material having a higher heat conductivity than that of constituent materials of the light emitting diode 15, and may be a silicon semiconductor substrate, ceramic substrate, or metal substrate. With the use of the material having a higher heat conductivity, the package substrate 17 can serve to emit heat generated from the light emitting diode 15 (as represented by dotted arrows).
However, the package substrate 17 having the higher heat conductivity also has a higher thermal expansion coefficient than that of the constituent materials of the light emitting diode 15. Therefore, when the package substrate 17 is cooled after being exposed to heat during a light emitting diode attachment process or driving process, an intensive thermal stress is generated at an interface between the light emitting diode 15 and the package substrate 17 as represented by arrows. The thermal stress may cause deterioration in the reliability of the light emitting diode 15, and in the worst case, may cause cracks in the light emitting diode 15, resulting in defective products.
To reduce the thermal stress generated at the interface, conventionally, a buffer material layer L has been employed between the light emitting diode 15 and the package substrate 17, as shown in FIG. 1. However, this solution is problematic because the buffer material layer L should be formed in a heat transfer path, although the buffer material layer L is preferable thermal stress reducing means. In other words, providing the buffer material layer L may cause deterioration in a heat emitting function of the package substrate.